Transmission apparatus, reception apparatus, transmission method, and reception method

ABSTRACT

In a communication system in which propagation path error tolerance is improved by switching the modulation method or error correction method adaptively according to the state of the propagation path, signals MX, MY, CX, and CY indicating the modulation method and error correction method used by the transmitting side are transmitted arranged at discrete locations within the same frame. By this means, the possibility of discretely arranged signals MX and MY, or CX and CY, both degrading is made low even if the transmit signal experiences fading or propagation path fluctuations. As a result, it is possible for the modulation method information signal and/or error correction method information signal to be restored correctly on the receiving side.

TECHNICAL FIELD

[0001] The present invention relates to a transmitting apparatus,receiving apparatus, transmission method, and reception method, and issuitable for application to a digital radio communication system inwhich the modulation method or error correction method is changedadaptively according to the propagation path environment, for example.

BACKGROUND ART

[0002] Conventionally, various kinds of system control are carried outin a radio communication system in order to perform communication withhigh quality and high efficiency. An example is a radio communicationsystem in which the modulation method or error correction method isswitched adaptively according to the state of the propagation path. Inthis kind of system, the current propagation path state is determinedbased on the SIR (Signal to Interference Ratio) of a signal that atransmitting/receiving apparatus receives from a communicating party, orthe like.

[0003] In practice, when the propagation path state is good, informationdata undergoes digital modulation using an M-ary modulation method witha large information bearing capacity per symbol, such as 64QAM, forexample, and is transmitted with the addition of an error correctioncode with a high degree of redundancy as an error correction method.When the propagation path state is poor, on the other hand, informationdata undergoes digital modulation using a modulation method with a smallinformation bearing capacity per symbol, such as 16QAM or QPSK, forexample, and is transmitted with the addition of an error correctioncode with a low degree of redundancy as an error correction method.

[0004] Thus, in this kind of radio communication system, it is necessaryto communicate to the receiving side the modulation method used tomodulate a transmit signal and the error correction method used forerror correction processing. A receiving apparatus has a plurality ofdemodulation sections corresponding to a plurality of modulationmethods, and a plurality of error correction decoding sectionscorresponding to a plurality of error correction methods, and restoresthe original data by executing demodulation processing and errorcorrection processing in accordance with a communicated modulationmethod information signal and error correction information signal.

[0005] An example of a known frame configuration for arranging signalsindicating a modulation method within a transmit frame is that describedin “Development of an Adaptive Modulation System for Land MobileCommunications—Outline of the Scheme—”, Hamaguchi et al., IEICECommunications Society Conference B-5-135 pp. 388, September 1997.

[0006]FIG. 1 shows this frame configuration. Located in order from thestart of the frame are one ramp symbol R, six synchronization symbolsSW, one pilot symbol P, one modulation method information symbol I, and18 data symbols DATA.

[0007] A receiving apparatus that receives a signal with this kind offrame configuration determines the modulation method of data symbolsDATA from modulation method information symbol I, and demodulates datasymbols DATA using a demodulation method corresponding to the determinedmodulation method.

[0008] If, in the receiving apparatus, determination of modulationmethod information symbol I or an error correction method informationsymbol (not shown) is incorrect, the data obtained by demodulation anddecoding of data symbols DATA will be incorrect. It is thereforeimportant for modulation method information and error correction methodinformation to be transmitted to the receiving apparatus correctly.

[0009] However, in radio communications, there is a risk of modulationmethod information and error correction method information beingerroneously determined on the receiving side due to noise, or fadingcaused by propagation path fluctuations, resulting in a reduction incommunication quality.

DISCLOSURE OF INVENTION

[0010] It is an object of the present invention to provide atransmitting apparatus, receiving apparatus, transmission method, andreception method that make it possible for the modulation method anderror correction method of a digitally modulated signal to be determinedcorrectly on the receiving side, enabling communication quality to beimproved.

[0011] This object is achieved by, in a communication system in whichpropagation path error tolerance is improved by switching the modulationmethod or error correction method adaptively according to the state ofthe propagation path, transmitting signals indicating the modulationmethod and error correction method used by the transmitting sidearranged at discrete locations within the same frame.

BRIEF DESCRIPTION OF DRAWINGS

[0012]FIG. 1 is a drawing showing a conventional transmit frameconfiguration;

[0013]FIG. 2 is a block diagram showing the configuration of atransmitting apparatus according to Embodiment 1 of the presentinvention;

[0014]FIG. 3 is a drawing showing a transmit frame configurationaccording to Embodiment 1;

[0015]FIG. 4 is an I-Q plane diagram provided to explain a case wheremodulation method information is QPSK modulated;

[0016]FIG. 5 is an I-Q plane diagram provided to explain a case whereerror correction method information is BPSK modulated;

[0017]FIG. 6 is a block diagram showing the configuration of a receivingapparatus according to Embodiment 1 of the present invention;

[0018]FIG. 7 is a block diagram showing the configuration of amodulation method and error correction method estimation section;

[0019]FIG. 8 is a drawing showing the received field strength of areceived signal when fading or propagation path fluctuations areexperienced;

[0020]FIG. 9 is a block diagram showing the configuration of atransmitting apparatus according to Embodiment 2;

[0021]FIG. 10(A) is a drawing showing a case where modulation methodinformation symbols and error correction method information symbols arearranged discretely in the frequency direction in an OFDM signal;

[0022]FIG. 10(B) is a drawing showing a case where modulation methodinformation symbols and error correction method information symbols arearranged discretely in the time direction in an OFDM signal; and

[0023]FIG. 11 is a block diagram showing the configuration of areceiving apparatus according to Embodiment 2.

BEST MODE FOR CARRYING OUT THE INVENTION

[0024] With reference now to the accompanying drawings, embodiments ofthe present invention will be explained in detail below.

[0025] (Embodiment 1)

[0026]FIG. 2 shows the configuration of a transmitting apparatusaccording to Embodiment 1 of the present invention. Transmittingapparatus 100 can select an error correction method and modulationmethod adaptively according to the state of the propagation path. Intransmitting apparatus 100, a transmit digital signal D1 is input to anerror correction A encoder 101 and error correction B encoder 102.

[0027] Error correction A encoder 101 and error correction B encoder 102perform error correction processing with different degrees ofredundancy. Specifically, error correction B encoder 102 performs errorcorrection processing with a higher degree of redundancy than errorcorrection A encoder 101, as a result of which error correction Bencoder 102 obtains error correction coded data with higher errortolerance. Error correction coded data obtained by error correction Aencoder 101 and error correction B encoder 102 is sent to a digitalsignal selection section 103.

[0028] Transmitting apparatus 100 has a modulation method and errorcorrection method decision section 104, to which a propagation pathestimation signal S1 is input. This propagation path estimation signalS1 is obtained based on the SIR (Signal to Interference Ratio), etc., ofa signal received from a communicating radio station by the receivingsection of transmitting apparatus 100 (not shown).

[0029] Modulation method and error correction method decision section104 decides the modulation method and error correction method inaccordance with propagation path estimation signal S1. In actuality,when the effects of fading fluctuations or noise are great, and apropagation path estimation signal S1 indicating that the propagationpath state is poor is input, a modulation method with good errortolerance such as BPSK (Binary Phase Shift Keying) or QPSK, for example,is selected as the modulation method, and an error correction methodwith a high degree of redundancy is decided on as the error correctionmethod.

[0030] Modulation method information S2 and error correction methodinformation S3 decided by modulation method and error correction methoddecision section 104 are sent to digital signal selection section 103, atransmission baseband signal selection section 106, and a controlinformation modulation section 105.

[0031] Digital signal selection section 103 selects the output of eithererror correction A encoder 101 or error correction B encoder 102 basedon error correction method information S3, and sends this output to aBPSK modulation section 107, QPSK modulation section 108, 16QAMmodulation section 109, and 64QAM modulation section 110.

[0032] Modulation sections 107 through 110 execute digital modulationprocessing on the digital signal input from digital signal selectionsection 103, and send signals that have undergone modulation processingto transmission baseband signal selection section 106. Transmissionbaseband signal selection section 106 selects a modulated signal fromamong the input plurality of modulated signals in accordance withmodulation method information S2. For example, when the propagation pathstate is poor and modulation method information S2 indicating BPSKmodulation or QPSK modulation is input, a BPSK modulated signal or QPSKmodulated signal is output selectively in accordance with this input.

[0033] The modulated signal selected by transmission baseband signalselection section 106, and signals indicating the modulation method anderror correction method modulated by control information modulationsection 105, are input to a frame configuration section 111. Controlinformation modulation section 105 executes modulation processing withhigh error tolerance, such as BPSK modulation or QPSK modulation, oninput signals. By this means, the error tolerance of signals relating tothe modulation method and error correction method, which is extremelyimportant information, is raised on the receiving side.

[0034] Frame configuration section 111 according to this embodimentconfigures a transmit frame as shown in FIG. 3, comprising, in orderfrom the start of the frame, one pilot symbol P, three consecutivemodulation method information symbols MX, three consecutive errorcorrection method information symbols CX, 128 data symbols DATA, a pilotsymbol P, data symbols DATA, a pilot symbol P, a 10-symbol unique wordUW, a pilot symbol P, modulation method information symbols MY, errorcorrection method information symbols CY, data symbols DATA, a pilotsymbol P, data symbols DATA, and a pilot symbol P.

[0035] Here, modulation method information symbols MX and modulationmethod information symbols MY are the same symbols, and error correctionmethod information symbols CX and error correction method informationsymbols CY are the same symbols. Thus, frame configuration section 111places modulation method information symbols MX and MY, and errorcorrection method information symbols CX and CY, discretely within thesame frame. In other words, modulation method information symbols MX andmodulation method information symbols MY are placed at differentlocations in the frame, and error correction method information symbolsCX and error correction method information symbols CY are placed atdifferent locations in the frame.

[0036] The way in which modulation of a consecutive plurality of symbols(in the case of this embodiment, three symbols) indicating modulationmethod information is carried out by control information modulationsection 105 will now be described. To consider the case where the threeconsecutive modulation method information symbols MX and MY are createdby QPSK modulation as shown in FIG. 4, there is a method whereby, forexample, signal point 201 is mapped at modulation method informationsymbols MX and MY when the information symbol modulation method is BPSKmodulation, signal point 202 is mapped in the case of QPSK modulation,signal point 203 is mapped in the case of 16QAM, and signal point 204 ismapped in the case of 64QAM.

[0037] As another way of performing modulation, there is a methodwhereby, for example, mapping is performed at 201, 202, and 203 intemporal order when the information symbol modulation method is BPSKmodulation, at 202, 204, and 203 in temporal order in the case of QPSKmodulation, at 204, 201, and 203 in temporal order in the case of 16QAM,and at 202, 204, and 201 in temporal order in the case of 64QAM.

[0038] The way in which modulation of a consecutive plurality of symbols(in the case of this embodiment, three symbols) indicating errorcorrection method information is carried out will now be described. Toconsider the case where the three consecutive error correction methodinformation symbols CX and CY are created by BPSK modulation as shown inFIG. 5, there is a method whereby, for example, signal point 301 ismapped at error correction method information symbols CX and CY whenerror correction method A is used, and signal point 302 is mapped whenerror correction method B is used.

[0039] As another way of performing modulation, there is a methodwhereby, for example, mapping is performed at 301, 302, and 302 intemporal order when error correction method A is used, and at 302, 301,and 301 in temporal order when error correction method B is used.

[0040] When the former method is used here (when mapping is performedwith signal points fixed), high-precision estimation is possible withfew symbols, and therefore the modulation method and error correctionmethod can be estimated on the receiving side by the simple method ofBPSK or QPSK modulation method detection. When the latter method is used(when signal points are mapped in temporal order), on the other hand,even if there are no symbols for time synchronization of thetransmitting apparatus and receiving apparatus, modulation methodinformation symbols and error correction method information symbols canbe used as symbols for time synchronization of the transmittingapparatus and receiving apparatus. On the other hand, complexcomputations known as serial correlation computations are necessary inthe receiving apparatus.

[0041] The signal output from frame configuration section 111 undergoesdigital-analog conversion and signal amplification processing by a radiosection 112, and is then transmitted by an antenna 113.

[0042]FIG. 6 shows the configuration of a receiving apparatus 500 thatreceives and demodulates a signal transmitted from transmittingapparatus 100. Receiving apparatus 500 executes predetermined radioreception processing such as amplification processing and analog-digitalconversion processing in a radio section 502 on a reception signalreceived by an antenna 501, thereby obtaining an orthogonal basebandsignal, and sends this signal to detection sections 503 through 506 anda modulation method and error correction method estimation section 507.

[0043] Detection sections 503 through 506 comprise a BPSK detectionsection 503, QPSK detection section 504, 16QAM detection section 505,and 64QAM detection section 506. The received baseband signals detectedby detection sections 503 through 506 are sent to a received digitalsignal selection section 508.

[0044] Modulation method and error correction method estimation section507 detects modulation method information symbols MX and MY, and errorcorrection method information symbols CX and CY, shown in FIG. 3, fromthe received orthogonal baseband signal, estimates the modulation methodand error correction method based on these information symbols MX, MY,CX, and CY, and sends estimation result S10 to received digital signalselection section 508 and a signal selection section 509.

[0045] Modulation method and error correction method estimation section507 is configured as shown in FIG. 7. That is to say, in modulationmethod and error correction method estimation section 507, the receivedorthogonal baseband signal output from radio section 502 is input to amodulation method and error correction method signal detection section520. Modulation method and error correction method signal detectionsection 520 performs coherent detection of modulation method informationsymbols MX and MY and error correction method information symbols CX andCY based on unique word UW contained in the received orthogonal basebandsignal, and by executing BPSK demodulation processing or QPSKdemodulation processing thereon, detects and demodulates modulationmethod information symbols MX and MY and error correction methodinformation symbols CX and CY.

[0046] A modulation method and error correction method information Xdetermination section 521 determines and detects modulation methodinformation symbols MX and error correction method information symbolsCX shown in FIG. 3 from the detected modulation method informationsymbols MX and MY and error correction method information symbols CX andCY. Similarly, a modulation method and error correction methodinformation Y determination section 522 determines and detectsmodulation method information MY and error correction method informationCY shown in FIG. 3 from the detected modulation method informationsymbols MX and MY and error correction method information symbols CX andCY.

[0047] Here, as is clear from FIG. 3, these modulation methodinformation symbols MX and error correction method information symbolsCX, and modulation method information symbols MY and error correctionmethod information symbols CY, are arranged discretely at separatelocations in a transmission frame, and are arranged at regularintervals. Therefore, modulation method and error correction methodinformation X determination section 521 and modulation method and errorcorrection method information Y determination section 522 can easilydetermine and detect these information symbols based on pilot symbols P,for example.

[0048] A modulation method and error correction method information Xreception power calculation section 523 calculates the reception powerof modulation method information symbols MX and error correction methodinformation symbols CX. Similarly, a modulation method and errorcorrection method information Y reception power calculation section 524calculates the reception power of modulation method information symbolsMY and error correction method information symbols CY. Actually, thelocations of modulation method information symbols MX and errorcorrection method information symbols CX, and modulation methodinformation symbols MY and error correction method information symbolsCY, arranged discretely within a frame, are detected based on pilotsymbols P and unique word UW, and the reception power of modulationmethod information symbols MX and error correction method informationsymbols CX, and the reception power of modulation method informationsymbols MY and error correction method information symbols CY, arecalculated.

[0049] A modulation method and error correction method decision section525 weights modulation method information MX and error correction methodinformation CX obtained by means of modulation method and errorcorrection method information X determination section 521 with thereception power obtained by means of modulation method and errorcorrection method information X reception power calculation section 523.Similarly, modulation method and error correction method decisionsection 525 weights modulation method information symbols MY and errorcorrection method information symbols CY obtained by means of modulationmethod and error correction method information Y determination section522 with the reception power obtained by means of modulation method anderror correction method information Y reception power calculationsection 524.

[0050] Then modulation method and error correction method decisionsection 525 decides the modulation method and error correction method byadding reception power weighted modulation method information symbols MXand MY and error correction method information symbols CX and CY. Thus,modulation method and error correction method estimation section 507detects the reception power at discrete locations for modulation methodinformation symbols MX and MY and error correction method informationsymbols CX and CY arranged discretely within a transmission frame, andby weighting and adding modulation method information symbols MX and MYand error correction method information symbols CX and CY according tothis reception power, obtains final modulation method information anderror correction method information.

[0051] Returning now to FIG. 6, receiving apparatus 500 will bedescribed. Received digital signal selection section 508 selects fromthe outputs of BPSK detection section 503, QPSK detection section 504,16QAM detection section 505, and 64QAM detection section 506, the outputcorresponding to the modulation method estimated by modulation methodand error correction method estimation section 507, and then sends thisoutput to an error correction A decoder 510 and error correction Bdecoder 511.

[0052] Reception demodulated signals decoded by error correction Adecoder 510 and error correction B decoder 511 using different errorcorrection methods are sent to signal selection section 509. Signalselection section 509 selects from error correction A decoder 510 anderror correction B decoder 511 the output corresponding to the errorcorrection method estimated by modulation method and error correctionmethod estimation section 507, and outputs this as the final receptiondecoded signal.

[0053] In the above configuration, transmitting apparatus 100 adaptivelyperforms digital modulation of data symbols DATA using modulationmethods with different error tolerance, and error correction processingusing error correction methods with different error tolerance, accordingto the state of the propagation path.

[0054] In addition, transmitting apparatus 100 transmits with modulationmethod information symbols MX and MY and error correction methodinformation symbols CX and CY arranged discretely within a transmitframe. Modulation method information symbols MX and MY and errorcorrection method information symbols CX and CY are transmittedmodulated using a modulation method with good error tolerance, such asBPSK modulation or QPSK modulation.

[0055] On receiving this transmit signal, receiving apparatus 500 firstcalculates the reception power of discretely arranged modulation methodinformation signals MX and MY and error correction method informationsignals CX and CY. As shown in FIG. 8, the reception power of a receivedsignal varies over time due to the effects of fading and so forth. As aresult, of discretely arranged modulation method information signals MXand MY and error correction method information signals CX and CY,modulation method information signal MX and error correction methodinformation signal CX may have low reception power (received fieldstrength), for example, while modulation method information signal MYand error correction method information signal CY have high receptionpower.

[0056] In general, a signal of higher reception power has a lower errorrate in demodulation, and therefore receiving apparatus 500 multipliesmodulation method information signal MX and error correction methodinformation signal CX, whose reception power is low, by a low-valuedweighting coefficient, and multiplies modulation method informationsignal MY and error correction method information signal CY, whosereception power is high, by a high-valued weighting coefficient. Theseadded values are then taken as final modulation method information anderror correction method information.

[0057] As a result, correct modulation method information and errorcorrection method information can be obtained even in the event ofpropagation path fluctuations or fading.

[0058] Receiving apparatus 500 selects data demodulated by means of ademodulation method corresponding to the acquired modulation methodinformation, and selects reception decoded data that has undergone errorcorrection decoding processing corresponding to the acquired errorcorrection method information, to obtain final receive data.

[0059] As a result, it is possible to obtain a signal that has beendemodulated and decoded by means of an appropriate modulation method andan appropriate error correction method, thereby enabling receptionquality to be improved.

[0060] A description will be given here of a discrete arrangement methodfor further improving the estimation precision for modulation method anderror correction method information. In order to restore modulationmethod and error correction method information correctly, the receivedfield strength of each information symbol need only be at or above acertain level. Thus, it is sufficient if there are symbols whosereceived field strength is at or above a certain level among discretelyarranged modulation method information and error correction methodinformation symbols.

[0061] Thus, in this embodiment, it is proposed that discretely arrangedtemporal locations be selected taking account of a time that is thereciprocal of the Doppler frequency. Specifically, if the maximumDoppler frequency stipulated in a radio communication system to whichtransmitting apparatus 100 and receiving apparatus 500 belong isdesignated fd, modulation method information signals MX and MY and errorcorrection method information signals CX and CY should be arranged atlocations separated by a time of approximately 1/fd.

[0062] By this means, even if the received field strength declines dueto fading, the decline in the received field strength at one or other ofthe locations of modulation method information signals MX and MY anderror correction method information signals CX and CY can be kept withinpermissible values, enabling the error rate of modulation methodinformation and error correction method information to be kept down.

[0063] For example, if discrete locations are selected as extremelyclose locations, when the received field strength declines due to fadingthe received field strength of all discretely arranged symbols willdecline, and the error rate of all modulation method and errorcorrection method information will increase. Considering this point, thelocations at which modulation method and error correction methodinformation is arranged may be decided simply as near the start, nearthe middle, or near the end, within a frame.

[0064] According to the above configuration, when the modulation methodor error correction method is switched adaptively according to the stateof the propagation path, the transmitting side transmits with modulationmethod information symbols MX and MY and error correction methodinformation symbols CX and CY arranged discretely within a transmitframe, and the receiving side detects the reception power of discretelyarranged modulation method information symbols MX and MY and errorcorrection method information symbols CX and CY at each location, findsthe final modulation method and error correction method by weighting thediscretely arranged modulation method information and error correctionmethod information according to the size of the reception power, andobtains a demodulated and decoded signal based thereon, thereby makingit possible to obtain a transmitting apparatus 100 and receivingapparatus 500 that enable degradation of communication quality to besuppressed even in the event of noise or propagation path fluctuations.

[0065] Also, by making modulation method information symbols MX and MYand error correction method information symbols CX and CY not a singlesymbol but a plurality of symbols (in the case of this embodiment, threesymbols), it is possible for modulation method information and errorcorrection method information to be transmitted more accurately.

[0066] Furthermore, by transmitting modulation method informationsymbols MX and MY and error correction method information symbols CX andCY modulated using BPSK modulation or QPSK modulation, which aremodulation methods tolerant of fading and propagation path fluctuations,it is possible for modulation method information and error correctionmethod information to be transmitted more accurately.

[0067] In this embodiment, a case has been described in which finalmodulation method information and error correction method information isobtained by weighting discretely arranged modulation method informationand error correction method information according to reception power,but the present invention is not limited to this, and it is alsopossible for only the modulation method information and error correctionmethod information with the larger reception power to be taken as thefinal modulation method information and error correction methodinformation. For example, when, as shown in FIG. 8, the reception powerof modulation method information MY and error correction methodinformation CY is higher than the reception power of modulation methodinformation MX and error correction method information CX, modulationmethod information MY and error correction method information CY may beselected.

[0068] Also, in this embodiment, a case has been described in which thetransmission power of symbols indicating the modulation method and errorcorrection method is made the same as the transmission power of datasymbols and pilot symbols, but if the transmission power (that is, themaximum signal amplitude) of symbols indicating the modulation methodand error correction method is made higher than the transmission power(maximum signal amplitude) of other symbols, it is possible formodulation method information and error correction method information tobe received with greater accuracy by the receiving side.

[0069] Moreover, in this embodiment, a case has been described in whicha transmit frame such as that shown in FIG. 3 is configured bytransmitting apparatus 100, but the frame configuration is not limitedto that shown in FIG. 3. Similarly, modulation method informationsymbols and error correction method information symbols are inserted asthree consecutive symbols at two discrete locations, but this is not alimitation.

[0070] Furthermore, the configurations of a transmitting apparatus,receiving apparatus, and modulation method and error correction methodestimation section according to the present invention are not limited tothose shown in FIG. 2, FIG. 6, or FIG. 7. In particular, in thisembodiment the number of locations at which modulation methodinformation and error correction method information is discretelyarranged is two, and therefore in the configuration of modulation methodand error correction method estimation section 507 in FIG. 7 twomodulation method and error correction method information determinationsections and two modulation method and error correction methodinformation reception power calculation sections are provided, but thesenumbers are in accordance with the number of discretely insertedmodulation method information symbols and error correction methodinformation symbols, and a number may be provided accordingly.

[0071] In addition, in this embodiment, a case has been described inwhich modulation method information and error correction methodinformation are transmitted, but the same kind of effect as in thisembodiment can also be obtained when the present invention is applied toa transmitting apparatus and receiving apparatus between which only oneof these is transmitted. For example, if the present invention is usedin a system in which only modulation method information is transmitted,it will be possible for modulation method information to be transmittedcorrectly to the receiving side.

[0072] (Embodiment 2)

[0073]FIG. 9, in which parts corresponding to those in FIG. 2 areassigned the same codes as in FIG. 2, shows the configuration of atransmitting apparatus according to Embodiment 2 of the presentinvention. Transmitting apparatus 800 transmits a transmit signalarranged in a mutually orthogonal plurality of subcarriers by means ofOFDM (Orthogonal Frequency Division Multiplexing).

[0074] Specifically, by executing serial/parallel conversion processingon the output of frame configuration section 111 by means of aserial/parallel conversion section (S/P conversion section) 801, andthen executing inverse Fourier transform processing on the parallelsignals resulting from this processing by means of an inverse Fouriertransform section (idft) 802, a transmit signal with the signalarrangement shown in FIG. 10(A) or FIG. 10(B) is formed. Divisions inthe frequency direction in FIG. 10(A) and FIG. 10(B) indicate subcarrierdemarcations. That is to say, FIG. 10(A) and FIG. 10(B) show examples inwhich a demodulated signal is transmitted using 10 mutually orthogonalsubcarriers.

[0075] In the example shown in FIG. 10(A), an error correction methodinformation symbol is arranged discretely in subcarriers of differentfrequency at the same time, and a modulation method information symbolis arranged discretely in subcarriers of different frequency at the sametime. By using this kind of arrangement, even if frequency selectivefading that causes a decline in the gain of a certain frequency occurson the propagation path, for example, the signal level of one errorcorrection method information symbol and modulation method informationsymbol is maintained, enabling an error correction method informationsignal and modulation method information signal with a signal levelgreater than or equal to a predetermined value to be obtained on thereceiving side.

[0076] In the example shown in FIG. 10(B), an error correction methodinformation symbol is arranged at different times in a subcarrier of thesame frequency, and a modulation method information symbol is arrangedat different times in a subcarrier of the same frequency. By using thiskind of arrangement, even if propagation path fluctuations occur overtime, for example, the signal level of an error correction methodinformation symbol and modulation method information symbol at aparticular point in time is maintained, enabling an error correctionmethod information signal and modulation method information signal witha signal level greater than or equal to a predetermined value to beobtained on the receiving side.

[0077] The configuration of a receiving apparatus that receives an OFDMsignal transmitted by transmitting apparatus 800 is shown in FIG. 11. InFIG. 11, in which parts corresponding to those in FIG. 6 are assignedthe same codes as in FIG. 6, receiving apparatus 1000 executes Fouriertransform processing on the output of radio section 502 by means of aFourier transform section (dft) 1001, and executes parallel/serialconversion of the signal resulting from Fourier transform processing bymeans of a parallel/serial conversion section (P/S conversion section)1002. As a result, a signal with the frame configuration shown in FIG. 3is obtained from the orthogonal frequency division multiplexed receivedsignal. Subsequent processing is the same as that described inEmbodiment 1.

[0078] According to the above configuration, when an OFDM signal isformed from a transmit signal containing an error correction methodinformation signal and modulation method information signal, andtransmitted, by arranging the error correction method information signaland modulation method information signal discretely in differentsubcarriers or at temporally separated locations in the same subcarrier,it is possible for an error correction method information signal andmodulation method information signal of the necessary signal level orhigher to be obtained on the receiving side. As a result, the modulationmethod and error correction method of a digitally modulated signal canbe determined correctly on the receiving side.

[0079] In this embodiment a case has been described in which OFDMmodulation processing is executed on output of frame configurationsection 111—that is, OFDM modulation processing is executed on a signalwith the frame configuration shown in FIG. 3—but the present inventionis not limited to this, and the key point is that, when an OFDM signalis formed from a transmit signal containing an error correction methodinformation signal and modulation method information signal, andtransmitted, the same kind of effect as in the above-describedembodiment can be obtained if the error correction method informationsignal and modulation method information signal are discretely arrangedin different subcarriers or at temporally separated locations in thesame subcarrier.

[0080] The present invention is not limited to the above-describedembodiments, and various variations and modifications may be possiblewithout departing from the scope of the present invention.

[0081] A transmitting apparatus according to the present invention has aconfiguration comprising a modulation method information signalgeneration section that generates an information signal relating to themodulation method of information symbols, an error correction methodinformation signal generation section that generates an informationsignal relating to the error correction method of information symbols, aframe forming section that forms a transmit frame by discretelyarranging a modulation method information signal and/or error correctionmethod information signal, and a transmission section that transmits thetransmit frame.

[0082] According to this configuration, since a modulation methodinformation signal and/or error correction method information signalare/is arranged discretely, the possibility is low that both discretelyarranged signals will degrade even if the transmit signal experiencesfading or propagation path fluctuations. As a result, it is possible forthe modulation method information signal and/or error correction methodinformation signal to be restored accurately on the receiving side.

[0083] A transmitting apparatus according to the present invention has aconfiguration wherein a modulation method information signal generationsection and/or error correction method information signal generationsection generate(s) a modulation method information signal or errorcorrection method information signal comprising a plurality of symbols.

[0084] According to this configuration, propagation path error toleranceis improved compared with the case where a modulation method informationsignal and/or error correction method information signal are/is formedby a single symbol, making it possible for the modulation methodinformation signal and/or error correction method information signal tobe restored more accurately on the receiving side.

[0085] A transmitting apparatus according to the present invention has aconfiguration wherein a frame forming section discretely arranges amodulation method information signal and/or error correction methodinformation signal at locations separated by a predetermined time ormore according to the Doppler frequency.

[0086] According to this configuration, even if the received fieldstrength declines due to fading, the decline in the received fieldstrength at one or other of the locations of discretely arrangedmodulation method information signals and error correction methodinformation signals can be kept within permissible values, enabling theerror rate of modulation method information and error correction methodinformation to be kept down even when fading occurs. For example, ifdiscrete locations are selected as extremely close locations, when thereceived field strength declines due to fading the received fieldstrength of all discretely arranged symbols will decline, and the errorrate of all modulation method and error correction method informationwill increase. In this configuration this point is taken intoconsideration, and discretely arranged locations are selected optimallytaking account of the Doppler frequency, which is closely linked tofading.

[0087] A transmitting apparatus according to the present invention has aconfiguration wherein a transmission section transmits a transmit framewith the maximum signal point amplitude of a modulation methodinformation signal and/or error correction method information signalmade larger than the maximum signal point amplitude of an informationsymbol.

[0088] According to this configuration, since the signal point intervalof a modulation method information signal and error correction methodinformation signal is increased, it is possible for the modulationmethod information signal and/or error correction method informationsignal to be restored more accurately on the receiving side.

[0089] A transmitting apparatus according to the present invention has aconfiguration whereby a modulation method information signal and/orerror correction method information signal are/is transmitted modulatedby means of BPSK modulation or QPSK modulation.

[0090] According to this configuration, since highly error tolerant BPSKmodulation or QPSK modulation is used as the information signal and/orerror correction method information signal modulation method, it ispossible for the modulation method information signal and/or errorcorrection method information signal to be restored more accurately onthe receiving side.

[0091] A transmitting apparatus according to the present invention has aconfiguration whereby a modulation method information signal and/orerror correction method information signal are/is arranged discretely ina mutually orthogonal plurality of subcarriers.

[0092] According to this configuration, even when frequency selectivefading occurs, the possibility is high that the decline in signal leveldue to fading will be small for the modulation method information signaland/or error correction method information signal of at least onesubcarrier among the modulation method information signals and/or errorcorrection method information signals arranged discretely in differentsubcarriers, and it is therefore possible for an error correction methodinformation signal and/or modulation method information signal of thenecessary signal level or higher to be obtained on the receiving side.

[0093] A receiving apparatus according to the present invention receivesand demodulates a received signal that contains an information signal, amodulation method information signal relating to the modulation methodof the information signal, and an error correction method informationsignal relating to the error correction method of the informationsignal, and wherein the modulation method information signal and errorcorrection method information signal are arranged at discrete locationswithin the same frame; and this receiving apparatus comprises areception power detection section that detects reception power for thediscretely arranged modulation method information signal and errorcorrection method information signal at the respective locations, adecision section that decides the modulation method and error correctionmethod by performing weighting according to the respective receptionpower on a modulation method information signal and error correctionmethod information signal arranged at a location corresponding toreception power detected by the reception power detection section, and asignal selection section that selects a demodulated signal obtained byexecuting demodulation processing and error correction processingcorresponding to the modulation method and error correction methoddecided by the decision section.

[0094] According to this configuration, attention is paid to the factthat errors are fewer in demodulation the higher the reception power atthe location of a signal, and the modulation method and error correctionmethod are decided by weighting a discretely arranged modulation methodinformation signal and error correction method information signal withreception power. As a result, the correct modulation method and errorcorrection method can be decided, and by performing demodulationprocessing and error correction processing in accordance therewith, ahigh-quality received signal can be obtained.

[0095] A receiving apparatus according to the present invention receivesand demodulates a received signal that contains an information signal, amodulation method information signal relating to the modulation methodof the information signal, and an error correction method informationsignal relating to the error correction method of the informationsignal, and wherein the modulation method information signal and errorcorrection method information signal are arranged at discrete locationswithin the same frame; and this receiving apparatus comprises areception power detection section that detects reception power for thediscretely arranged modulation method information signal and errorcorrection method information signal at the respective locations, adecision section that decides the modulation method and error correctionmethod by selecting a modulation method information signal and errorcorrection method information signal arranged at a locationcorresponding to reception power detected by the reception powerdetection section, and a signal selection section that selects ademodulated signal obtained by executing demodulation processing anderror correction processing corresponding to the modulation method anderror correction method decided by the decision section.

[0096] According to this configuration, attention is paid to the factthat errors are fewer in demodulation the higher the reception power atthe location of a signal, and of the discretely arranged modulationmethod information signals and error correction method informationsignals, the modulation method and error correction method of thesignals with higher reception power are selected. As a result, accuratemodulation method and error correction method signals with few errors indemodulation can be obtained, and by performing demodulation processingand error correction processing in accordance therewith, a high-qualityreceived signal can be obtained.

[0097] A transmission method according to the present inventiongenerates a modulation method information signal relating to themodulation method of information symbols and also generates an errorcorrection method information signal relating to the error correctionmethod of information symbols, forms a transmit frame by discretelyarranging a modulation method information signal and/or error correctionmethod information signal, and transmits the transmit frame.

[0098] According to this method, since a modulation method informationsignal and/or error correction method information signal are/is arrangeddiscretely, the possibility is low that both discretely arranged signalswill degrade even if the transmit signal experiences fading orpropagation path fluctuations. As a result, it is possible for themodulation method information signal and/or error correction methodinformation signal to be restored accurately on the receiving side.

[0099] A reception method according to the present invention receivesand demodulates a received signal that contains an information signal, amodulation method information signal relating to the modulation methodof the information signal, and an error correction method informationsignal relating to the error correction method of the informationsignal, and wherein the modulation method information signal and errorcorrection method information signal are arranged at discrete locationswithin the same frame; and this reception method detects reception powerfor the discretely arranged modulation method information signal anderror correction method information signal at the respective locations,decides the modulation method and error correction method by selecting amodulation method information signal and error correction methodinformation signal arranged at a location corresponding to detectedreception power, and selects a demodulated signal obtained by executingdemodulation processing and error correction processing corresponding tothe decided modulation method and error correction method.

[0100] According to this method, attention is paid to the fact thaterrors are fewer in demodulation the higher the reception power at thelocation of a signal, and of the discretely arranged modulation methodinformation signals and error correction method information signals, themodulation method and error correction method of the signals with higherreception power are selected. As a result, accurate modulation methodand error correction method signals with few errors in demodulation canbe obtained, and by performing demodulation processing and errorcorrection processing in accordance therewith, a high-quality receivedsignal can be obtained.

[0101] As described above, according to the present invention, in acommunication system in which propagation path error tolerance isimproved by switching the modulation method or error correction methodadaptively according to the state of the propagation path, bytransmitting signals indicating the modulation method and errorcorrection method used by the transmitting side arranged at discretelocations within the same frame, it is possible for the modulationmethod and error correction method of a digitally modulated signal to bedetermined correctly on the receiving side, enabling communicationquality to be improved.

[0102] This application is based on Japanese Patent Application No.2001-356400 filed on Nov. 21, 2001, entire contents of which areexpressly incorporated by reference herein.

INDUSTRIAL APPLICABILITY

[0103] The present invention is applicable, for example, to a digitalradio communication system in which the modulation method or errorcorrection method is changed adaptively according to the propagationpath environment or the like.

1. A transmitting apparatus comprising: a modulation method informationsignal generation section that generates an information signal relatingto a modulation method of an information symbol; an error correctionmethod information signal generation section that generates aninformation signal relating to an error correction method of aninformation symbol; a frame forming section that forms a transmit frameby discretely arranging said modulation method information signal and/orerror correction method information signal; and a transmission sectionthat transmits said transmit frame.
 2. The transmitting apparatusaccording to claim 1, wherein said modulation method information signalgeneration section and/or error correction method information signalgeneration section generate(s) said modulation method information signalor error correction method information signal comprising a plurality ofsymbols.
 3. The transmitting apparatus according to claim 1, whereinsaid frame forming section discretely arranges said modulation methodinformation signal and/or error correction method information signal atlocations separated by a predetermined time or more according to aDoppler frequency.
 4. The transmitting apparatus according to claim 1,wherein said transmission section makes a maximum signal point amplitudeof said modulation method information signal and/or error correctionmethod information signal larger than a maximum signal point amplitudeof said information symbol, and transmits said transmit frame.
 5. Thetransmitting apparatus according to claim 1, wherein said modulationmethod information signal and/or error correction method informationsignal are/is transmitted modulated by means of BPSK modulation or QPSKmodulation.
 6. The transmitting apparatus according to claim 1, whereinsaid transmit frame forming section forms a transmit frame so that saidmodulation method information signal and/or error correction methodinformation signal are/is arranged discretely in a mutually orthogonalplurality of subcarriers.
 7. A receiving apparatus that receives anddemodulates a received signal that contains an information signal, amodulation method information signal relating to a modulation method ofan information signal, and an error correction method information signalrelating to an error correction method of an information signal, andwherein said modulation method information signal and said errorcorrection method information signal are arranged at discrete locationswithin the same frame; said receiving apparatus comprising: a receptionpower detection section that detects reception power for discretelyarranged said modulation method information signal and error correctionmethod information signal at their respective locations; a decisionsection that decides a modulation method and error correction method byperforming weighting according to reception power respectively on saidmodulation method information signal and error correction methodinformation signal arranged at a location corresponding to receptionpower detected by said reception power detection section; and a signalselection section that selects a demodulated signal obtained byexecuting demodulation processing and error correction processingcorresponding to a modulation method and error correction method decidedby said decision section.
 8. A receiving apparatus that receives anddemodulates a received signal that contains an information signal, amodulation method information signal relating to a modulation method ofan information signal, and an error correction method information signalrelating to an error correction method of an information signal, andwherein said modulation method information signal and said errorcorrection method information signal are arranged at discrete locationswithin the same frame; said receiving apparatus comprising: a receptionpower detection section that detects reception power for discretelyarranged said modulation method information signal and error correctionmethod information signal at their respective locations; a decisionsection that decides a modulation method and error correction method byselecting said modulation method information signal and error correctionmethod information signal arranged at a location corresponding toreception power detected by said reception power detection section; anda signal selection section that selects a demodulated signal obtained byexecuting demodulation processing and error correction processingcorresponding to a modulation method and error correction method decidedby said decision section.
 9. A transmission method comprising the stepsof: generating a modulation method information signal relating to amodulation method of an information symbol and also generating an errorcorrection method information signal relating to an error correctionmethod of an information symbol; forming a transmit frame by discretelyarranging said modulation method information signal and/or errorcorrection method information signal; and transmitting said transmitframe.
 10. A reception method of receiving and demodulating a receivedsignal that contains an information signal, a modulation methodinformation signal relating to a modulation method of an informationsignal, and an error correction method information signal relating to anerror correction method of an information signal, and wherein saidmodulation method information signal and said error correction methodinformation signal are arranged at discrete locations within the sameframe; said reception method comprising the steps of: detectingreception power for discretely arranged said modulation methodinformation signal and error correction method information signal attheir respective locations; deciding a modulation method and errorcorrection method by selecting said modulation method information signaland error correction method information signal arranged at a locationcorresponding to detected reception power; and selecting a demodulatedsignal obtained by executing demodulation processing and errorcorrection processing corresponding to a decided modulation method anderror correction method.